Materials generally used in the semiconductor process are required to have a high purity and a corrosion resistance, and thus quartz has been usually used as fixtures for semiconductor processes. However, as the processing temperature and the size of silicon wafer in semiconductor processes are increased, quartz incurs many problems as fixtures for semiconductor processes. That is, quartz has a thermal expansion coefficient difference with a silicon wafer and a low frature strength, and thus has limitations to be applied to the next-generation semiconductor process in which a 450 mm-level silicon wafer and a 20 nm-level line width are expected to be proceed. Accordingly, it is required that an alternative material is developed. The reaction bonded SiC has been recognized as a typical candidate material for high temperature semiconductor processes, which may substitute for quartz.
A typical reaction bonded SiC fixtures has a high content of metallic impurities, which is approximately from 10 ppm to 100 ppm, and thus reaction bonded SiC with a high purity is essentially needed in order to use reaction bonded SiC as a material for high temperature semiconductor processes. SiC fixtures for the use in high temperature semiconductor processes is generally manufactured by sintering process using SiC powders with a purity of less than 10 ppm at the high temperature, but as the super-high integration proceeds in the semiconductor process, it is likely that the purity required in the SiC powders used as a starting material for SiC fixtures used in high temperature semiconductor processes is also increased. For the applications a reaction bonded SiC fixtures for high temperature semiconductor processes, a chemical vapor deposition (CVD) SiC coating process has been used to make a high purity SiC layer having an impurity content of 1 ppm or less on the surface of the reaction bonded SiC, but there are problems in a CVD SiC coating layer such as the occurrence of cracks that generally caused by repeated semiconductor high temperature processes.
In a general method of manufacturing a reaction bonded SiC, the reaction bonded SiC is prepared by infiltrating molten Si into a green body made of SiC powders and a carbon source material, and the purity of SiC powders used as a raw material needs to be increased in order to increase the purity of the reaction bonded SiC. Recently, the application of an SiC single crystal substrate that may be substituted for an Si semiconductor in the semiconductor field used for high temperature and high power applications has been increased, and an SiC single crystal has been also applied as a substrate for the GaN epitaxial growing for LED. In a method of preparing SiC single crystals, SiC powders used as a raw material are generally sublimated into the gas phase at an ultra high temperature and then condensed to grow the resulting SiC single crystals. The biggest problem in manufacturing SiC single crystals is generation of defects occurring during the preparation of SiC crystals, and it is essential to use SiC powders with a high purity in order to prepare SiC single crystals with a low defect concentration. Further, granular SiC powders with a high purity are generally used in growing SiC single crystals by a sublimation method.
Accordingly, in order to manufacture a SiC fixtures with a high purity, it is essentially required that SiC powders used as a raw material thereof become highly pure.
According to methods for manufacturing SiC powders which have been reported until now, various silicon sources and carbon sources in the solid, liquid and gas phases are used to synthesize SiC powders under vacuum or inert gas atmospheres at a high temperature. The Acheson method that is a representative method of manufacturing SiC powders may be an economical method as a process of manufacturing alpha-phase SiC powders. However, the resulting SiC powders have a purity of 99.99% or less since a series of powdering processes including pulverizing the SiC ingots manufactured by the Acheson method need to be additionally performed, the powdering process of which provides an opportunity to incorporate impurities; and as a result, an additional purification process such as acid treatment needs to be performed to increase the purity of resulting SiC powders. Accordingly, SiC powders manufactured by the general method are not appropriate for use as raw powders to manufacture SiC fixtures for high temperature semiconductor processes and SiC single crystals that require SiC powders with a purity higher than 99.999. In addition, there are methods for manufacturing beta-phase SiC powders with a high purity by a gas phase reaction using gas phase raw materials including a silicon source and a carbon source in the gas phase, but the productivity is low, manufacturing costs are high, and there are many difficulties in manufacturing granular SiC powders. Although there are methods of manufacturing SiC powders by thermal pyrolysis of organic silicon compounds such as a methyl hydrogen silane-based compound simultaneously including silicon source and carbon source [U.S. Pat. Nos. 4,571,331 and 4,676,966], SiC powders manufactured by the methods are highly pure, but resulting SiC powders having a size from 0.01 um to 1 um, and are usually used in the preparation of SiC fixtures by a hot pressing process for high-purity semiconductor processes as well as LED process.
Recently, methods of using organic compounds of liquid phase silicon source and carbon source or using a liquid phase carbon source and a solid phase silicon source such as silica have been known in order to synthesize SiC powders with a high purity. Synthesis methods of SiC powders with a high purity using liquid phase organic compounds as a silicon source and a carbon source are disclosed in Japanese Patent Application Laid Open Nos. 2002-326876, 2006-25937 and 2006-256937, U.S. Pat. Nos. 5,863,325 and 6,627,169, and the like. As the methods of using liquid phase organic compounds, disclosed are methods of manufacturing SiC powders with a high purity having a various size by performing the carbothermal reduction process under vacuum or inert gas atmospheres such as argon (Ar) at a high temperature using a hybrid SiO2-C mixture manufactured by a sol-gel process using liquid phase carbon compounds with a high purity, such as such as phenol resin, xylene-based resin or the like and various kinds of liquid phase silicon compounds with a high purity, such as ethyl silicate, silicon alkoxide, or silane. However, the process requires a heat treatment process under vacuum or inert gas atmospheres at a high temperature from 1,700° C. to 2,100° C. for a long time, and the time required for the high temperature heat treatment is long and the yield of synthesized SiC powders using an expensive liquid phase silicon source is low, and thus a market based on the mass production has not yet been formed due to high manufacturing costs.
Recently, a direct carbonization method of manufacturing granular SiC powders with a high purity by directly reacting a metallic silicon with a solid phase carbon has been disclosed in US Patent Application Publication No. 2009-0220788. This method discloses that ultra pure granular SiC powders with extremely low content of nitrogen, boron, and aluminum may be synthesized by heating silicon powders and carbon powders under vacuum atmosphere at a temperature of 1,200° C. for 12 hours and then maintaining under an atmosphere of 10−5 torr or less at 2,250° C. for 1 to 2 hours, and SiC single crystals having a low defect concentration and excellent insulating property may be manufactured by using the same. This method makes it possible to synthesize granular SiC powders, but is regarded as problematic in terms of mass production since granular SiC powders are manufactured under ultra high temperature and high vacuum.